Drainage Modeling

The automated analysis system uses a drainage model based on a physical approach. It works by simulating a drainage runoff physically. Each pixel gets an initial water value of one, and for each pixel the path of this simulated fluid is calculated using a steepest descent approach. Drainage along this path is accumulated and if it meets another path already found, its drainage is added to that path downstream of where it met. In this approach, drainage of every pixel in the image is determined. In addition, every pixel in the image has a value that represents the drainage accumulation (area draining) into that pixel. Thresholding the results at different accumulation values yields the drainage delineation that is used for this system. 

Since this is a physically-based approach rather than a pure topographical (shape only) approach, it has the advantage of not only delineating the channels, but providing a measure of the drainage area flowing through them. This is believed to be very important for accurate stream ordering calculations. However, the presence of noise and/or data artifacts still can cause problems. Channels can be interrupted; because of noise or artifacts, even high flow drainage channels can have nowhere to flow. To correct for these difficulties, an algorithm is used for the filling of depression areas in the data.Single pixel pits are filled by raising the height of the single pixel pit to a position halfway between the lowest and the next lowest neighbor.

The drainage modeling produces an accumulated drainage map, Strahler branch ordering map and a watershed map. These maps are used by the knowledge bases in conjunction with the elevation data. The adjacent tables indicate the attribution associated with the computed drainage model.

An example of a Strahler branch order drainage plot overlaid on synthetic shaded relief. Blue is lowest order, with green, orange, and red representing increasingly higher orders.

Network Properties

Parameter	Description
Drainage Density	Mean channel length/unit area
Stream Frequency	Number of stream segments by order
Bifurcation Ratio	Avg. ratio of Order N to Order N+1
Channel Slope	Slope in drainage channels

Relief Properties

Watershed Properties

Parameter	Description
Area	Fundamental Measure
Perimeter Length	Fundamental Measure
Circularity Ratio	Total basin area / circle area with same perimeter
Elongation Ratio	Diameter of same area circle / max basin length
Form Factor	Basin area / basin length squared
Shape	Basin length squared/basin area